Couch to half marathon: sixteen weeks

Sixteen weeks buys two things, not a third

A half marathon rewards two capacities: running 18 km comfortably, and absorbing carbohydrate without your gut objecting. Sixteen weeks is enough to build both from a 10K base. It is not enough to build the base as well.

So the entry condition is not negotiable: 45 minutes continuous, four times a week, or a finished 10K. Starting from nothing does not make this plan harder, it makes it the wrong plan. If that is you, go back to the 10K block.

If you have already raced a half and run 18 km regularly, this is a maintenance block rather than a build. The rest of the piece assumes the base is there and the plan has one central lever.

The long run stops at 18 km because the fade is decided early

You do not need to run 21.1 km in training. The race is 21.1 km; the training is the sixteen weeks that get you there. The longest run here is 18 km, three weeks out, and it exists to teach pacing and gut tolerance rather than to prove distance.

Runners who fade at 16 km are usually the ones whose long runs were twenty seconds per kilometre too fast, week after week. The fade is accumulated, not sudden, which means it is decided long before the last 5 km.

Finish the last 3 km of the week 10 and week 13 long runs at half marathon effort. That is the only dress rehearsal you need. The distance around it is what makes the rehearsal count.

A long run that takes more than three days to recover from is a race you did not enter. Which is why the distance around it matters as much as the run itself.

Volume is built in the easy runs, not the long one

Weekly volume climbs from 26 to 42 km. At peak the long run is less than half of that total, and the rest is easy running that exists to add frequency without adding a session that needs recovering from.

Four runs in most weeks, five in three of them. The fifth is always short and easy. If it costs you the long run, cut it. Weeks 4, 8 and 12 are lighter on purpose; week 15 is the first taper week, not an absorb week, and treating it as one by adding a session is the most common way a good block goes wrong.

Three weeks build, one absorbs. The lighter weeks are where the previous three become fitness, and fitness is not the only thing the race requires.

Fuel is trainable, and the evidence is smaller than the marketing

Runs over about 75 minutes are worth fuelling: 30 to 60 grams of carbohydrate an hour, taken in small amounts rather than all at once. Practise on at least three long runs, using the products you plan to race with.

The performance gain at this distance is modest. In a study of eighteen well-trained half marathoners, carbohydrate produced a trivial 14-second improvement over placebo, and three runners got gut discomfort that cost them 105 seconds. Rehearsal is not about finding speed; it is about not being one of the three.

A gel is not a shortcut. It is an insurance policy you have tested, and it only becomes visible once the volume comes off.

The taper is where the fitness shows up

Two weeks, volume down by 40 to 50 percent, intensity unchanged. A meta-analysis of taper studies found the best results came from cutting volume by 41 to 60 percent over two weeks while keeping intensity and frequency.

You will feel heavy and start doubting the plan. That is normal in a taper and it is not a sign of lost fitness. What is not normal is pain arriving in the last month.

What breaks first is the week you skip

The jump from 10K volume to half volume is the biggest single increase here, and it is where most problems appear. If you miss more than a week, drop back to the last week you completed rather than picking up where the calendar says you should be.

Pain in one spot that persists, pain that changes your gait, or pain that is worse the day after every run is a reason to get assessed. Training through it rarely shortens the interruption. Equipment is the last decision, and the least important.

Warning signs to see a professional

The shoe has two jobs, and they are not interchangeable

A protected long-run shoe does the weekly distance; a lighter race shoe handles the last few long runs and the day itself. The long-run pair should feel boring by week eight, which is the point. The race pair should feel faster than it feels comfortable.

Do not race in a shoe you have not run at least 30 km in. Carbon plates change how the calves and Achilles load, and a half marathon is a long way to discover that. Which leaves race day, where nothing new is allowed.

Race day is a pacing exercise you have already rehearsed

Even pacing, with the first 5 km five to ten seconds per kilometre slower than target. Take fuel at 40 to 45 minutes even if you do not feel like it, because appetite arrives late and the deficit arrives early.

Nothing new on race day: not the shoes, not the gel flavour, not the breakfast. The race tests the sixteen weeks, not your improvisation.